Array-based system and method for inspecting a workpiece with backscattered ultrasonic signals

ABSTRACT

A method and an array-based system for inspecting a structure are provided that can identify unacceptable levels of porosity, microcracking or defects attributable to thermal damage. The inspection system includes a two-dimensional array of ultrasonic transducers, and an array controller configured to trigger at least one ultrasonic transducer to emit an ultrasonic signal into the structure. The array controller is also configured to receive data representative of backscattered signals preferentially received by at least one ultrasonic transducer from a portion of the structure offset from the at least one ultrasonic transducer that was triggered to emit the ultrasonic signal.

TECHNICAL FIELD

Embodiments relate generally to a system and method for inspecting astructure and, more particularly, to an array-based system and methodfor detecting, for example, porosity, microcracks or thermal damage viaa single-sided ultrasonic inspection of a structure.

BACKGROUND

Non-destructive inspection (NDI) of structures involves thoroughlyexamining a structure without harming the structure or requiring itssignificant disassembly. Non-destructive inspection is typicallypreferred to avoid the schedule, labor, and costs associated withremoval of a part for inspection, as well as avoidance of the potentialfor damaging the structure. Non-destructive inspection is advantageousfor many applications in which a thorough inspection of the exteriorand/or interior of a structure is required. For example, non-destructiveinspection is commonly used in the aircraft industry to inspect aircraftstructures for any type of internal or external damage to or defects(flaws) in the structure. Inspection may be performed duringmanufacturing or after the completed structure has been put intoservice, including field testing, to validate the continued integrityand fitness of the structure.

During NDI, one or more sensors may move over the portion of thestructure to be examined, and receive data regarding the structure.Various types of sensors may be used to perform non-destructiveinspection. For example and without limitation, a pulse-echo (PE),through transmission (TT), or shear wave sensor may be used to obtainultrasonic data, such as for thickness gauging, detection of laminardefects and/or crack detection in the structure.

In some circumstances, only a single surface of the structure may beaccessible for inspection purposes, which may limit the potentialinspection techniques. For example, in the field, access to interiorsurfaces of the structure may be restricted, requiring disassembly ofthe structure and introducing additional time and labor. Similarly,during manufacture, one of the surfaces may be disposed upon a mandreland be inaccessible, at least without undesirable and time-consumingdisassembly.

While single-sided inspection techniques, such as PE, can be employed todetect disbonds, delaminations, cracks or other substantial defects, itmay be difficult to detect porosity in certain situations, such assituations in which the structure under inspection is ultrasonicallycoupled to another structure, such as a mandrel or other backingmaterial, absent a TT inspection technique. In this regard, in PE, theamplitude of the reflection from the back surface, i.e., the surfaceopposite the inspection sensor, is used as a gage to determine thepercent of porosity by comparing the reflection from the back surface ofthe structure under inspection with standard data gathered from priorinspections of reference samples of known porosity. Accordingly,porosity may be difficult to detect and/or quantify, especially inconjunction with structures that are only amenable of single-sidedinspection and are ultrasonically coupled to another structure, sincethe ultrasonic coupling will reduce the reflection from the back surfaceby an unknown amount. Such difficulties in accurately detecting and/orquantifying porosity may be problematic in composite manufacturingprocesses in which it is desirable to monitor the quality of thecomposite material including, for example, the porosity of the compositematerial to insure that the manufacturing process is performing in thedesired manner.

While it is generally desirable to detect porosity during or followingmanufacture, it is similarly desirable to be able to identifymicrocracking or thermal damage in the field or otherwise once thecomposite material has been placed in service. Microcracking can occurdue to fatigue or thermal cycling of composites. Microcracks generallyconsist of multiple small cracks in the resin and fibers of a compositestructure. Typical crack sizes are in the 0.010 inch to over 0.200 inchrange. Thermal damage may be attributable to various sources and, inaerospace applications, may be attributable to engine exhaustimpingement, overheated components in a confined space, or firesinvolving a component. Regardless of its source, thermal damage maydegrade the matrix properties and the interface between matrix materialand the embedded fibers, thereby leading to undesirable changes.

Conventionally, laboratory-based methods have been employed to detectand determine the extent of thermal damage. Unfortunately, thelaboratory-based methods cannot generally be performed in the field andoftentimes require disassembly or other rework of the compositestructure. As such, non-destructive methods of detecting thermal damagehave been developed, including infrared (IR) spectroscopy, laser pumpedflorescence and high frequency eddy current inspection. However, IRspectroscopy and laser pumped fluorescence are generally localizedtechniques that may be capable of measuring thermal damage within one tothree plies of the surface. For thicker structures, plies must generallybe successively removed and then the remaining structure re-inspected todetect thermal damage deeper within a structure, thereby increasing thetime and cost required for an inspection. High frequency eddy currentinspection measures the change in resistance in the matrix material,such as that change in resistance attributable to overheating. However,high frequency eddy current inspection is also a near surface inspectionmethod and generally cannot be utilized if the composite structureincludes lightening strike protection. High frequency eddy currentinspection may be also disadvantageously sensitive to conductivestructures in the immediate vicinity of the inspection area and to thegeometry of the structure.

Ultrasonic PE has also been employed in an effort to detect thermaldamage. However, it may be difficult to detect thermal damage until thethermal damage is sufficiently substantial so as to result in discretedelaminations. Accordingly, thermal damage may be difficult to detectand/or quantify via ultrasonic PE at earlier stages.

In some instances, the thermal damage is not visible. Additionally,conventional nondestructive inspection techniques may not detect thethermal damage, particularly in instances in which the compositematerial must be inspected from a single side for at least the reasonsdescribed above in conjunction with porosity detection. Moreover, evenin instances in which it is suspected that a composite structure hassuffered thermal damage, such as a result of surface charring ordiscoloring, a portion of the composite structure may be removed andreplaced. However, the removal and replacement may later prove to becompletely unnecessary in instances in which the composite structurehas, in fact, not been thermally damaged. Alternatively, the removal andreplacement may later prove to be excessive in instances in which alarger portion of the composite structure is removed and replaced out ofprecaution than has been actually thermally damaged.

Additionally, while handheld inspection probes have been developed, itis sometimes desirable to inspect larger portions of a structure thanthose that can be quickly or efficiently inspected with a handheldprobe. As such, robotic inspection scanners have been developed.However, robotic scanners can be somewhat expensive and may not beavailable in all locations, such as on the field or other remotelocations, at which it is desirable to inspect a structure.

Thus, it would be desirable to be able to detect porosity, microcrackingand/or thermal damage in an efficient manner, even in instances in whichlarger regions of a structure are to be inspected.

SUMMARY

A method and an array-based system for inspecting a workpiece aretherefore provided that have embodiments that address at least some ofthe deficiencies identified with conventional techniques. In thisregard, the method and system of at least some embodiments can identifyunacceptable levels of porosity, microcracking or defects attributableto thermal damage, even in instances in which the workpiece can only beinspected from a single side. As such, the method and array-based systemof at least some embodiments are suitable for inspection, either duringmanufacturing or once a workpiece has been placed in service in thefield. Moreover, by utilizing an array of ultrasonic transducers, thesystem and method of at least some embodiments can inspect a workpiecein an efficient manner.

According to one aspect, a system is provided that includes atwo-dimensional array of ultrasonic transducers configured to bedisposed upon a surface of a structure. The system of this embodimentalso includes an array controller configured to trigger at least oneultrasonic transducer to emit an ultrasonic signal into the structure.The array controller is also configured to receive data representativeof backscattered signals preferentially received by at least oneultrasonic transducer from a portion of the structure offset from the atleast one ultrasonic transducer that was triggered to emit theultrasonic signal. In one embodiment, the two-dimensional array ofultrasonic transducers includes a plurality of ultrasonic transducersthat are each positioned to emit ultrasonic signals that propagate alonga predefined axis of propagation that intersects the surface of thestructure at a non-orthogonal angle. In this embodiment, the arraycontroller may be configured to trigger the same ultrasonictransducer(s) to both emit an ultrasonic signal into the structure andto receive the backscattered signals from the structure.

According to another embodiment, a system is provided that includes anarray controller configured to trigger at least one first linear arrayof ultrasonic transducers to emit ultrasonic signals into the structure.The array controller of this embodiment is also configured to receivedata representative of backscattered signals received by at least onesecond linear array of ultrasonic transducers. One of the first andsecond linear arrays of ultrasonic transducers includes a linear arrayof ultrasonic transducers extending in a first direction. However, theother of the first and second linear arrays of ultrasonic transducersincludes at least a pair of the linear arrays of ultrasonic transducersthat extend in different directions relative to one another. The systemof this embodiment also includes a computing device configured todetermine a material property of the structure based upon the datarepresentative of the backscattered signals received by the at least onesecond linear array of ultrasonic transducers.

According to another aspect, a method is provided for determining amaterial property of the structure. The method initially triggers atleast one first linear array of ultrasonic transducers to emitultrasonic signals into the structure. The method also receives datarepresentative of backscattered signals received by at least one secondlinear array of ultrasonic transducers. One of the at least one firstand second linear arrays of ultrasonic transducers include a lineararray of ultrasonic transducers extending in the first direction. Theother of the at least one first and second linear arrays of ultrasonictransducers includes at least a pair of the linear arrays of ultrasonictransducers extending in different directions relative to one another.The method also determines a material property of the structure basedupon the data representative of the backscattered signals received bythe at least one second linear array of ultrasonic transducers.

In one embodiment, the at least one first linear array of ultrasonictransducers may include at least a pair of linear arrays extending inone direction and at least a pair of linear arrays extending in adifferent direction. In this embodiment, the at least one second lineararray of ultrasonic transducers may extend between at least one pair ofthe first linear arrays. In this embodiment, the pairs of linear arraysmay bound at least one ultrasonic transducer through which the at leastone second linear array of ultrasonic transducers may extend.

In one embodiment, the at least one second linear array of ultrasonictransducers includes at least a pair of linear arrays extending in onedirection and at least a pair of linear arrays extending in a differentdirection. In this regard, the at least one first linear array ofultrasonic transducers may extend between the at least one pair of thesecond linear array. In one embodiment, the pairs of linear arrays boundat least one ultrasonic element with the at least one first linear arrayof ultrasonic transducers extending through the at least one ultrasonictransducer that is bounded by the pairs of linear arrays.

By determining and then analyzing the backscattered signals, theporosity, microcracking and/or thermal damage at a particular locationcan be more accurately assessed and anomalies can be detected. Byutilizing backscattered signals and, accordingly, permitting inspectionfrom a single side of the workpiece, the method and apparatus of atleast some embodiments do not require disassembly of the workpiece and,instead, permit inspection, while the workpiece remains upon a mandrelor other tooling, such as during manufacture, or remains in an assembledform, such as while in the field or otherwise in service.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described certain embodiments in general terms, referencewill now be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

FIG. 1 is a perspective view of an ultrasonic inspection system inaccordance with one embodiment;

FIG. 2 is a side view of a two-dimensional array of an ultrasonicinspection system in accordance with one embodiment;

FIG. 3 is a schematic representation of the orientation of an ultrasonictransducer relative to a structure in accordance with one embodiment;

FIG. 4A graphically represents the signals received by an ultrasonictransducer during the inspection of a structure with little porosity,few microcracks and little heat damage in accordance with oneembodiment;

FIG. 4B graphically represents the signals received by an ultrasonictransducer during the inspection of a structure with more substantialporosity, more microcracks and/or more substantial heat damage inaccordance with one embodiment;

FIG. 5 graphically depicts the digitization, rectification and summationof the signals received by an ultrasonic transducer during theinspection of a structure with more substantial porosity, moremicrocracks and/or more substantial heat damage in accordance with oneembodiment;

FIG. 6 graphically depicts the digitization, rectification and summationof the signals received by an ultrasonic transducer during theinspection of a structure with little porosity, few microcracks andlittle heat damage in accordance with one embodiment;

FIG. 7 is a side view of a two-dimensional array of an ultrasonicinspection system in accordance with another embodiment;

FIG. 8 is a schematic representation of several rows and columns of atwo-dimensional array which depicts the positional relationship of therows and columns of ultrasonic transducers that transmit and receiveultrasonic signals in accordance with one embodiment;

FIG. 9 is a schematic side view of the portion of the two-dimensionalarray of FIG. 8 taken along line 9-9 which illustrates the backscattering of the ultrasonic signals in response to porosity,microcracking or thermal damage in accordance with one embodiment;

FIG. 10 is a schematic representation of several rows and columns of atwo-dimensional array which depicts the positional relationship of therows and columns of ultrasonic transducers that transmit and receiveultrasonic signals in accordance with another embodiment;

FIG. 11 is a is a schematic side view of the portion of thetwo-dimensional array of FIG. 10 taken along line 11-11 whichillustrates the back scattering of the ultrasonic signals in response toporosity, microcracking or thermal damage in accordance with anotherembodiment; and

FIG. 12 is a flowchart of operations performed in accordance with oneembodiment of the present disclosure.

DETAILED DESCRIPTION

Certain aspects of the disclosure now will be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the inventions are shown. Indeed, theseaspects may be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will satisfy applicablelegal requirements. Like numbers refer to like elements throughout.

An ultrasonic inspection system 10 by which a structure may be inspectedaccording to at least one embodiment is shown in FIG. 1. The ultrasonicinspection system 10 includes a two-dimensional array 12, an arraycontroller 14, and a computing device 16. The ultrasonic inspectionsystem can inspect a variety of structures formed of various materials.Structures that may be inspected with an embodiment of an inspectionsystem may include, but are not limited to, composites such as carbonfiber or graphite reinforced epoxy (Gr/Ep) composites or foam filledcomposites, non-ferromagnetic metals (e.g. aluminum alloy, titaniumalloy, or aluminum or titanium hybrid laminates such as GLARE or Ti/Gr),ferromagnetic metals, plastics, ceramics, polymers and virtually allsolids, semi-solids and even liquids. A structure being inspected may beany myriad of shapes and/or sizes and used in a variety of applications,including aircraft, marine vehicles, automobiles, spacecraft and thelike, as well as buildings. For example, the structure may be a foamfilled hat stiffener or hat stringer. Moreover, the structure may beinspected prior to assembly, such as for porosity, or followingassembly, such as for microcracking and/or thermal damage, as describedbelow.

The ultrasonic inspection system 10 is generally configured forsingle-sided inspection of the workpiece as a result of its relianceupon backscattered signals. As such, the ultrasonic inspection apparatusis operable to inspect structures in instances in which the oppositeside of the structure is inaccessible. For example, the ultrasonicinspection system is operable to inspect structures during manufacturein instances in which the structure is supported upon a mandrel or othertooling with the opposite or back side of the structure facing themandrel or other tooling. Similarly, the ultrasonic inspection apparatusis operable to inspect structures following deployment even if only asingle side is accessible, thereby potentially reducing instances inwhich the structure must be disassembled and/or removed from the fieldfor inspection.

The two-dimensional array 12 may be flexible sensor array that includesultrasonic sensors 18 bonded to a flexible mat 20 in a regularly spacedpattern. In one embodiment, each ultrasonic sensor includes a transducerelement that is operable as a pulse-echo inspection sensor that bothsends and receives ultrasonic waves. The transducer elements can befabricated, for example and as known, from a polymer-basedpiezo-electric material called polyvinylidene fluoride (PVDF).

The periphery of the flexible mat 20 may define a gasket or groove 21,as shown in FIG. 2, for contacting an inspected structure andtemporarily adhering the flexible sensor array to the structure whenintervening air is removed by an optional vacuum system accessory of theultrasonic inspection system 10. Alternatively, the flexible mat can betaped or otherwise temporarily adhered to an inspected structure by anadhesive material. Additionally, the flexible mat can be held in placeby any suitable means, such as, without limitation, by hand, by a clampor bracket or the like.

The sensor array 12 is illustrated in FIG. 1 to include two hundred andfifty six sensors disposed in rows and columns regularly spaced by onequarter of one inch to define a square grid pattern that is four incheswide on each side thereof. It should be understood that thesedescriptions relate nonetheless to sensor arrays having other numbers ofsensors, other disposition patterns, and other pattern spacings. Forexample, these descriptions relate as well to a sensor array having onethousand and twenty fours sensors arranged in rows and columns regularlyspaced by one quarter of one inch to define a square grid pattern thatis eight inches wide on each side thereof. For further example thesedescriptions relate to sensor arrays defining hexagonal patterns andother patterns. Thus, these descriptions relate to a sensor array havingany number of sensors arranged in any two-dimensional pattern.

The sensor array 12 may also include a plurality of segmented delaylines 22, as shown in FIG. 2 which depicts one exemplary linear array,e.g., one row or column, from the sensor array. In this regard, thesensor array and, more particularly, the flexible mat 20, may include arubber pad positioned between the ultrasonic transducers 18 and thestructure. The rubber pad may be divided into a plurality of segmentswith each segment being associated with and positioned in alignment witha respective ultrasonic transducer. As such, the segmented pad serves toat least partially isolate the ultrasonic signals transmitted andreceived by each ultrasonic transducer from those transmitted andreceived by the other ultrasonic transducers. As also shown in FIG. 2,the sensor array may include an acoustic backing material 24, such asepoxy resin containing high “Z” metal powder, positioned proximate to,but on the opposite side of the ultrasonic transducers from thestructure that is to be inspected, thereby further directing the signalsemitted by the ultrasonic transducers toward the structure or, at least,reducing the ultrasonic signals emitted by the ultrasonic transducersthat propagate in a direction away from the structure. Otherconventional acoustic backing materials include a soft encapsulent, suchas epoxy resin, containing tungsten which serves as an acousticabsorber. A low melting point alloy, such as InPb, and one or morepowders having high impedance characteristics, e.g., tungsten andcopper, may also be used as an acoustic backing material. Depending uponthe application and inspection environment, a couplant, such as anultrasonic gel or water, may also be applied between the sensor arrayand the surface of the structure to provide a good path from thetransducer into the structure.

The sensor array 12 is disposed in electronic communication with thearray controller 14, for example by way of a cable 23 that can includeany number of electrically conductive wires or by way of a wirelesscommunications link. The array controller generally energizes eachultrasonic sensor 18 to send an ultrasonic pulse into an inspectedstructure and then receives data, typically in the form of an electricalsignal, generated by the sensor when an ultrasonic echo signal returnsfrom the structure.

The computing device 16, such as a personal computer, workstation or thelike, receives the data from the array controller 14 and may process,store and/or graphically display the data for interpretation by a userin order to, for example, identifying damages in an inspected structure.The display of the data by the computing and display device may beprovided in various forms. For example, the computing device of FIG. 1provides a C-scan image. However, the computing device may display thedata as an A-scan, a B-scan, or in other manners, if so desired.

In one embodiment depicted in FIG. 3 in which a single transducer 18 isshown for purposes of illustration, each transducer is oriented in sucha manner as to introduce ultrasonic signals that propagate along an axis26 positioned at an offset angle 28 relative to a predefined referencedirection oriented normal to the surface of the structure that faces theinspection apparatus. The offset angle may have various predefinedvalues, but is typically an acute, non-zero angle, such as between 5°and 45° and, in one embodiment, between 5° and 15° relative to thepredefined reference direction. The ultrasonic transducer may emitultrasonic signals at any of a plurality of different frequencies.Typically, the frequency of the ultrasonic signals varies in an inverserelationship to the thickness of the workpiece to be inspected. Forexample and without limitation, the ultrasonic transducer may transmitsignals having a frequency of 10 MHZ for the inspection of thinnerstructures and a frequency of either 2.25 MHZ or 3.5 MHZ for theinspection of thicker structures. In one embodiment, however, theultrasonic transducer emits signals having a frequency of 5 MHZ.

In operation, the sensor array 12 is positioned relative to theworkpiece at a predefined location. The array controller 14 thenactuates one or more ultrasonic transducers 18 to transmit an ultrasonicsignal into the workpiece. Although the array controller can actuate theultrasonic transducer in various manners, the array transducer of oneembodiment includes an ultrasonic pulser receiver module or card foractuating the ultrasonic transducer(s). As described, the ultrasonicsignals transmitted by the transducer propagate along an axis 26 that isdisposed at an offset angle 28 from a normal to the surface of theworkpiece. Upon encountering defects, such as porosity, a microcrack orthermal damage, a portion of the ultrasonic signals are backscattered asshown by the arcuate lines 27 of FIG. 3, and at least a portion of thebackscattered signals are received and detected by the ultrasonictransducer. A large defect, such as a delamination, a disbond or thelike, will not tend to scatter the signals, but will reflect the signalsaway from the transducer because of the angle. The backscattered signalsattributable to the interaction of the ultrasonic signals with anysingle pore, microcrack or any single void or other defect created by,for instance, thermal impingement may be generally relatively small, butmeasurable. In order to evaluate the porosity, microcracking or thethermal damage of the workpiece at the respective location, the sum ofthe backscattered signals attributable to a plurality of the pores, aplurality of microcracks or a plurality of other defects at therespective locations, such as all of the pores, microcracks or all otherdefects in the beam path, may be determined. In this regard, the sum ofthe backscattered signals is informative since it may be only in theaggregate that the effects of porosity or microcracking or of thedefects attributable to thermal damage upon the structure in thatlocation can generally be assessed.

In this regard, the array controller 14 generally receives the outputfrom the ultrasonic transducer(s) 18 over a predefined period of timewith the output of the ultrasonic transducer(s) being representative ofthe amplitude of the signals received by the ultrasonic transducer(s)over the predetermined period of time. The array controller, in turn,provides data representative of the output of the ultrasonictransducer(s) to the computing device 16. In one embodiment, thecomputing device includes a digitizer for converting analog signalsprovided by the ultrasonic transducer(s) to corresponding digitalsignals. Additionally, the computing device can include a rectifier forrectifying the signals produced by the ultrasonic transducer(s) eitherprior to or following analog-to-digital conversion. As shown in FIG. 4A,the digitized and rectified signals representative of the amplitude ofthe backscattered signals received by an ultrasonic transducer aresmaller when a structure having little porosity, few microcracks andlittle other damage is suspected. Alternatively, the digitized andrectified signals representative of the amplitude of the backscatteredsignals received by the ultrasonic transducer are larger over time whenthe structure has more substantial porosity, more microcracks or hassuffered heat damage as shown in FIG. 4B.

By integrating or summing the signals, e.g., once digitized andrectified, representative of the amplitude of the backscattered signalsreceived by the ultrasonic transducers 18 over a predetermined period oftime, the computing device 16 can determine a measure representative ofthe degree of porosity, microcracking or thermal damage of the structureat the respective location. The computing device can then compare thesum of the backscattered signals received by the ultrasonic transducerwith a predefined threshold, and the computing device can provide anindication of whether the structure at the respective location has anunacceptable degree of porosity, an unacceptable amount of microcrackingor an unacceptable amount of thermal damage based upon the relationshipof the sum of the backscattered signals received by the ultrasonictransducer to the predefined threshold. Typically, the predefinedthreshold is set to a value such that the sum of the backscatteredsignals received by the ultrasonic transducer over the predefined periodat any location is indicative of an unacceptable level of porosity,microcracking or thermal damage if the sum exceeds a predefinedthreshold. Conversely, if the sum of the backscattered signals receivedby the ultrasonic transducer is less than the predefined threshold, thestructure will generally be found to have acceptable levels of porosity,microcracking and thermal damage at the respective location. The valueof the predefined threshold may vary, depending upon the application,the loads that are anticipated to be placed upon the structure and thetolerance of the structure and/or the application to the structuralchanges occasioned by porosity, microcracking or thermal damage, amongother factors.

Although the predefined threshold may be defined in various manners, thepredefined threshold may be determined by inspecting several samplesconstructed of the same materials and having the same thickness andconfiguration as the structure, but having different known levels ofporosity, microcracking and/or thermal damage—some of which being knownto be acceptable and others of which being known to be unacceptable. Bycomparing the measure representative of the degree of porosity,microcracking or thermal damage for each of the samples and determiningthose measures that are reflective of acceptable samples and thosereflective of unacceptable samples, the threshold representative of thedividing line between acceptable and unacceptable levels of porosity,microcracking or thermal damage may be predefined.

The predetermined time period over which the backscattered signalsreceived by the ultrasonic transducer 18 are summed generallycorresponds to the thickness of the structure or, at least, thethickness of the portion of the structure that is desirably inspected.In this regard, the predetermined time period is generally set to equalor slightly exceed the time required for ultrasonic signals to propagatethrough the structure or at least that portion of the structure that isdesired to be inspected and to then return to the ultrasonic transducer.While the predetermined time period can have a wide range of valuesdepending upon the thickness of the structure or at least the thicknessof that portion of the structure that is desirably inspected, thepredetermined time period is typically one to a few microseconds.

By way of example, the leftmost graphs in FIGS. 5 and 6 illustrate thedigitized output of an ultrasonic transducer 18 in terms of the relativeultrasonic amplitude of the backscattered signals over a period of 350microseconds during the inspection of structures having a porosity of6.15% and 0%, respectively. The relative ultrasonic amplitude of thebackscattered signals represent the voltage produced by the ultrasonictransducer (E.G., piezoelectric transducer as the ultrasonic (stress)waves impinge upon the face of the transducer. The relative ultrasonicamplitude is typically measured in digitizer units with the actualvoltage being unimportant so long as no changes are made to theultrasonic transducer during a test. In turn, the rightmost graphs ofFIGS. 5 and 6 depict the same output following rectification. Byintegrating the area under the respective graphs, a measure of 39,043 isobtained for the structure having a porosity of 6.15% and a measure of13,116 is obtained for the structure having a porosity of 0%. As such,FIGS. 5 and 6 graphically illustrate the relationship between the areaunder the curve and the porosity (or likewise, microcracking or thermaldamage) of a structure.

While the summation of the amplitudes of the backscattered signalsreceived by the ultrasonic transducer 18 over a predetermined period oftime permits the aggregate effect of pores, microcracks or defects to bedetermined in instances in which the effect of a single pore (or a smallnumber of pores), a single microcrack (or a small number of microcracks)or a single defect (or a small number of defects) would otherwise beinsignificant, the reliance predominantly upon backscattered signals,such as a result of the propagation of the ultrasonic signals at anoffset angle relative to the normal to the surface of the structure asprovided by the embodiment of FIG. 2, also advantageously permits theultrasonic inspection system to obtain reliable results indicative ofthe porosity, microcracking or other damage of the structure. In termsof the embodiment of FIGS. 2 and 3, reflections from the front surfaceor back surface of the structure or from larger delaminations ordisbonds within the structure cause a portion of the ultrasonic signalsto be reflected. As a result of the propagation of the ultrasonicsignals of this embodiment at the offset angle relative to the normal tothe surface of the structure, the reflections of the ultrasonic signalsdo not return to the transducer, but are reflected at an angle basedupon Snell's Law as schematically represented by FIG. 3. By avoiding thereflection of the ultrasonic signals from the front and back surfaces ofthe structure or from delaminations or disbonds from being detected bythe ultrasonic transducer, the backscattered signals received by theultrasonic transducer are not washed out or otherwise renderedinsignificant as a result of the receipt of reflected signals having alarger, sometimes much larger, amplitude.

In the embodiment depicted in FIG. 2, the sensor array 12 includes aplurality of ultrasonic transducers 18 positioned so as to transmitsignals at an offset angle 28 relative to the surface of the structureto be inspected. The array controller 14 may trigger the ultrasonictransducers of the sensor array in various manners. For example, thearray controller can trigger individual ultrasonic transducers such thata first ultrasonic transducer emits an ultrasonic signal and receivesany resulting backscattered signals from the structure. This process maythen be repeated for each or at least a plurality of the ultrasonictransducers of the sensor array. Alternatively, the array controller cansimultaneously trigger a plurality of ultrasonic transducers, such as alinear array, e.g., a row or a column, of ultrasonic transducers, toemit ultrasonic signals. The array controller of this embodiment canalso cause a plurality of ultrasonic transducers, such as another lineararray of ultrasonic transducers extending in a different direction, toreceive the return signals from the structure. For example, the arraycontroller may cause a row of ultrasonic transducers to emit ultrasonicsignals and a column of ultrasonic signals to receive the return signalsfrom the structure. Of the return signals received by the ultrasonictransducers, the return signals received by the ultrasonic transducerthat is at the point of intersection of the linear arrays of ultrasonictransducers that were driven to emit and receive signals will berepresentative of the porosity, microcracks or damage of the structureproximate to, such as underlying, the respective transducer element,with the return signals received by the other ultrasonic transducersgenerally being of less relevance and, in many embodiments, simplyignored. For a sensor array having ultrasonic transducers arranged in aplurality of rows and columns, a row of ultrasonic transducers may bedriven to emit ultrasonic signals with the columns of the sensor arraybeing sequentially enabled to receive return signals in order toindividually evaluate the backscattered signals received by eachultrasonic transducer of the respective row. This process can then berepeated for a plurality of rows, such as each row, as a sensor array.As such, the ultrasonic inspection system of this embodiment canindividually evaluate the porosity, microcracking and/or damage of thestructure proximate to, such as underlying, each ultrasonic transducerof the sensor array.

In another embodiment, the sensor array 12 includes a plurality ofultrasonic transducers 18, but the ultrasonic transducers are positionedso as to emit ultrasonic signals that propagate in a direction generallyorthogonal to the surface of the structure to be inspected. For example,FIG. 7 depicts one linear array of ultrasonic transducers, e.g., one rowor column, configured in accordance with this other embodiment. Althoughthe ultrasonic transducers are positioned to emit ultrasonic signals ina direction generally orthogonal to the surface of the structure, theultrasonic transducers can be driven in such a manner as topreferentially detect backscattered signals. In this regard, the arraycontroller 14 can trigger one or more ultrasonic transducers to emitultrasonic signals. The array controller can then direct one or moreultrasonic transducers to receive the return signals from the structure.However, the array controller is configured such that the ultrasonictransducers that are directed to receive the return signals aredifferent than, but proximate to, the ultrasonic transducers that aretriggered to emit ultrasonic signals.

For example, the array controller 14 may direct that a single ultrasonictransducer 18 (i.e., an emitting transducer) emit ultrasonic signalsinto the structure. The array controller of this embodiment may thendirect that one or more ultrasonic transducers (i.e., receivingtransducers) that are different than, but adjacent to the emittingtransducer receive the return signals occasioned as a result of thetransmission of ultrasonic signals by the emitting transducer. As aresult of the difference in position of the receiving transducers fromthe emitting transducer, the return signals received by the ultrasonictransducers generally include backscattered signals, such as thosesignals backscattered from porosity, microcracking or damage at alocation proximate to, such as underlying, the emitting transducer.

While the array controller 14 may direct such emission and reception onan individual transducer basis, the array controller of one embodimentdirects that linear arrays of ultrasonic transducers 18, such as rows orcolumns of ultrasonic transducers, be directed to transmit or receive.As shown in FIG. 8, the array controller may trigger a first lineararray of ultrasonic transducers (i.e., an emitting array 18 e), such asa first column of ultrasonic transducers, to emit ultrasonic signalsinto the structure. The array controller of this embodiment may alsodirect a pair of linear arrays of ultrasonic transducers (i.e.,receiving arrays 18 r) that extend in different directions from oneanother, such as a row and a column of ultrasonic transducers, toreceive return signals from the structure. In the illustratedembodiment, for example, the array controller directs at least twocolumns of ultrasonic transducers and at least two rows of ultrasonictransducers to receive return signals from the structure. The receivingarrays are generally spaced from one another with the emitting arraysbeing positioned between a pair of the receiving arrays.

In the illustrated embodiment, for example, the rows and columns ofultrasonic transducers that are directed to receive the return signals,i.e., the receiving arrays 18 r, bound or surround one or moreultrasonic transducers 18 b. As also depicted by the illustratedembodiment, the column of ultrasonic transducers that is triggered toemit ultrasonic signals, i.e., the emitting array 18 e, thereforeincludes the ultrasonic transducer that is bounded by those rows andcolumns of ultrasonic transducers that are directed to receive thereturn signal. As such, the return signals received by the rows andcolumns of ultrasonic transducers that bound the ultrasonic transducerare generally considered to receive backscattered signals that arerepresentative of the porosity, microcracking or thermal damageproximate to, such as underlying, the ultrasonic transducer that isbounded. In this regard, FIG. 9 schematically depicts a manner in whichsome of the ultrasonic signals emitted by a respective ultrasonictransducer are backscattered (as shown by reference number 30) toadjacent ultrasonic transducers.

In still another embodiment, the array controller 14 of FIG. 1 maytrigger two or more linear arrays of ultrasonic transducers (i.e.,emitting arrays 18 e) that extend in different directions, such as a rowand a column of ultrasonic transducers, to concurrently emit ultrasonicsignals. In the embodiment illustrated in FIG. 10, for example, thearray controller directs that a pair of columns of ultrasonictransducers and a pair of rows of ultrasonic transducers simultaneouslytransmit ultrasonic signals into the structure. The array controller ofthis embodiment also directs at least one and, in the illustratedembodiment, a pair of linear arrays of ultrasonic transducers (i.e.,receiving arrays 18 r) such as a row and a column of ultrasonictransducers, to receive the return signals from the structure. Ininstances in which the emitting arrays are spaced apart from oneanother, the receiving array(s) may be positioned therebetween. In ananalogous manner to that described above, the emitting arrays may bound,or surround, one or more ultrasonic transducers 18 b. In thisembodiment, each receiving array may include the ultrasonic transducerthat is bounded. As a result, the return signals received by thereceiving arrays will be indicative of the porosity, microcracking orthermal damage proximate to, such as underlying, the ultrasonictransducer that is bounded as a result of the back scattering of theultrasonic signals 30 as shown in FIG. 11.

By thereafter repeating the foregoing process with respect to differentcombinations of the rows and columns of ultrasonic transducers 18 whichbound different ultrasonic transducers 18 b, the porosity, microcrackingor thermal damage of the structure that underlie each of a plurality ofultrasonic transducers may be determined.

As described above, the results of the inspection can be processed inmany different manners. For example, the sum of the amplitude of thebackscattered signals within a predefined period of time at eachrespective location can be stored and/or analyzed to identifylocation(s) which would appear to have an undesirable amount ofporosity, microcracking or thermal damage. In this regard, the arraycontroller 14 can transmit the data, such as in either a wireline orwireless manner, to the computing device 16 for subsequent analysis,such as to identify location(s) which would appear to have anundesirable amount of porosity, microcracking or thermal damage. Forexample, by comparing the sum of the amplitude of the backscatteredsignals received by the ultrasonic transducer over a predeterminedperiod of time at each location, the computing device can provide awarning, an alarm or the like to the operator of the inspectionapparatus during the course of the inspection of any location(s) thatappear to have an unacceptable degree of porosity, microcracking orthermal damage. Moreover, the results can be presented in a variety ofmanners, including in a numerical format representative of the sum ofthe amplitudes of the backscattered signals over a predetermined periodof time at the different locations or graphically in which the sums ofthe amplitudes of the backscattered signals at each location aregraphically depicted.

As noted above, the ultrasonic inspection system 10 can be deployed forvarious applications, including the inspection of a structure 12 duringmanufacture, in which case the ultrasonic inspection apparatus wouldgenerally inspect the structure for porosity, or following placement ofthe structure into service in the field, in which instances theultrasonic inspection apparatus would generally inspect the structurefor the effects of microcracking or thermal damage. Advantageously, theultrasonic inspection system is generally capable of injecting theultrasonic signals into the structure and receiving the backscatteredsignals from the structure, even in instances in which the surface ofthe structure that faces the ultrasonic inspection apparatus has beenprimed, painted or includes lightening strike protection. Moreover, byutilizing a two-dimensional sensor array 12, the inspection system caninspect larger portions of a structure in an efficient and rapid manner.

Many modifications and other embodiments will come to mind to oneskilled in the art to which the disclosure pertains having the benefitof the teachings presented in the foregoing descriptions and theassociated drawings. For example, the array controller 14 and thecomputing device 16 have been depicted as separate elements.Alternatively, the computing device and the array controller may beembodied by the same device. Additionally, while ultrasonic transducers18 have been described by both transmit and receive ultrasonic signals,the ultrasonic transducers may be comprised of distinct ultrasonictransmitters and ultrasonic transducers in other embodiments. Therefore,it is to be understood that the disclosure is not to be limited to thespecific embodiments disclosed and that modifications and otherembodiments are intended to be included within the scope of the appendedclaims. Although specific terms are employed herein, they are used in ageneric and descriptive sense only and not for purposes of limitation.

1. A system comprising: a two-dimensional array of ultrasonictransducers configured to be disposed upon a surface of a structure; andan array controller configured to trigger at least one a first array ofemitting ultrasonic transducers to emit an ultrasonic signal into thestructure, the array controller also configured to receive datarepresentative of back scattered signals preferentially received by atleast one a second array of receiving ultrasonic transducers from aportion of the structure offset from the at least one first array ofemitting ultrasonic transducers that was triggered to emit theultrasonic signal, the first array of emitting ultrasonic transducersand the second array of receiving ultrasonic transducers extending indifferent directions.
 2. A system according to claim 1 wherein thetwo-dimensional array of ultrasonic transducers comprises a plurality ofthe first array of emitting ultrasonic transducers are positioned toemit ultrasonic signals that propagate along a predefined axis ofpropagation that intersects the surface of the structure at anon-orthogonal angle.
 3. A system according to claim 1 wherein the firstarray of emitting ultrasonic transducers comprises a first linear arrayof ultrasonic transducers and the second array of receiving ultrasonictransducers comprise at least one second linear array of ultrasonictransducers, wherein one of the at least one first and second lineararrays of ultrasonic transducers comprises a linear array of ultrasonictransducers extending in a first direction, and wherein the other of theat least one first and second linear arrays of ultrasonic transducerscomprises at least a pair of the linear arrays of ultrasonic transducersextending in different directions relative to one another.
 4. A systemaccording to claim 3 wherein the at least one first linear array ofultrasonic transducers comprises at least a pair of linear arraysextending in one direction and at least a pair of linear arraysextending in a different direction, wherein the pairs of linear arraysbound at least one ultrasonic transducer of the two-dimensional array,and wherein the at least one second linear array of ultrasonictransducers extends through the at least one ultrasonic transducer thatis bounded by the pairs of linear arrays.
 5. A system according to claim3 wherein the at least one second linear array of ultrasonic transducerscomprises at least a pair of linear arrays extending in one directionand at least a pair of linear arrays extending in a different direction,wherein the pairs of linear arrays bound at least one ultrasonictransducer of the two-dimensional array, and wherein the at least onefirst linear array of ultrasonic transducers extends through the atleast one ultrasonic transducer that is bounded by the pairs of lineararrays.
 6. A system comprising: an array controller configured totrigger at least one a first array of emitting ultrasonic transducers toemit ultrasonic signals into a structure, the array controller alsoconfigured to receive data representative of backscattered signalsreceived by a plurality second array of receiving ultrasonic transducersfrom a portion of the structure offset from the first array of emittingultrasonic transducers, the first array of emitting ultrasonictransducers and the second array of receiving ultrasonic transducersextending in different directions.
 7. A system according to claim 6wherein the first array of emitting ultrasonic transducers comprises afirst linear array of ultrasonic transducers and the second array ofreceiving ultrasonic transducers comprise at least one second lineararray of ultrasonic transducers, wherein one of the at least one firstand second linear arrays of ultrasonic transducers comprises a lineararray of ultrasonic transducers extending in a first direction, andwherein the other of the at least one first and second linear arrays ofultrasonic transducers comprises at least a pair of the linear arrays ofultrasonic transducers extending in different directions relative to oneanother.
 8. A system according to claim 7 wherein the at least one firstlinear array of ultrasonic transducers comprises at least a pair oflinear arrays extending in one direction and at least a pair of lineararrays extending in a different direction.
 9. A system according toclaim 8 wherein the at least one second linear array of ultrasonictransducers extends between at least one pair of the first lineararrays.
 10. A system according to claim 8 wherein the pairs of lineararrays bound at least one ultrasonic transducer, and wherein the atleast one second linear array of ultrasonic transducers extends throughthe at least one ultrasonic transducer that is bounded by the pairs oflinear arrays.
 11. A system according to claim 10 wherein the at leastone first linear array of ultrasonic transducers extends between atleast one pair of the second linear arrays.
 12. A system according toclaim 10 wherein the pairs of linear arrays bound at least oneultrasonic transducer, and wherein the at least one first linear arrayof ultrasonic transducers extends through the at least one ultrasonictransducer that is bounded by the pairs of linear arrays.
 13. A systemaccording to claim 7 wherein the at least one second linear array ofultrasonic transducers comprises at least a pair of linear arraysextending in one direction and at least a pair of linear arraysextending in a different direction.
 14. A method comprising: triggeringat least one a first array of emitting ultrasonic transducers to emitultrasonic signals into a structure; receiving data representative ofbackscattered signals received by a plurality second array of receivingultrasonic transducers from a portion of the structure offset from thefirst array of emitting ultrasonic transducers, the first array ofemitting ultrasonic transducers and the second array of receivingultrasonic transducers extending in different directions; anddetermining a material property of that portion of the structureassociated with the emitting ultrasonic transducer based upon the datarepresentative of the backscattered signals received by the plurality ofreceiving ultrasonic transducers.
 15. A method according to claim 14wherein the first array of emitting ultrasonic transducers comprises afirst linear array of ultrasonic transducers and the second array ofreceiving ultrasonic transducers comprise at least one second lineararray of ultrasonic transducers, wherein one of the at least one firstand second linear arrays of ultrasonic transducers comprises a lineararray of ultrasonic transducers extending in a first direction, andwherein the other of the at least one first and second linear arrays ofultrasonic transducers comprises at least a pair of the linear arrays ofultrasonic transducers extending in different directions relative to oneanother.
 16. A method according to claim 15 wherein the at least onefirst linear array of ultrasonic transducers comprises at least a pairof linear arrays extending in one direction and at least a pair oflinear arrays extending in a different direction.
 17. A method accordingto claim 15 wherein the at least one second linear array of ultrasonictransducers comprises at least a pair of linear arrays extending in onedirection and at least a pair of linear arrays extending in a differentdirection.